1. Field of the Invention
This invention relates generally to apparatus and method for inspection of elongated material. More specifically, this invention relates to apparatus and method for inspecting elongated material such as strands, sheets, bundles or webs for the presence of surface irregularities, count of irregularities within a given length, and angle of irregularities such as in the case of crimped fiber. Data obtained from such inspection may be used for quality control purposes.
This invention is particularly useful in monitoring production lines where continuous lengths of sheet or fibrous material is produced. Although various inspection uses will be apparent to those skilled in the art the present invention will be described herein mainly in reference to the production of fiber tow which has been evenly crimped. Such fiber tow, e.g., cellulose acetate filter tow, is mechanically crimped for various reasons known to those skilled in the art. Due to factors beyond the control of the machines or their operators, however, sometimes there are lengths of the tow where crimp does not appear, or the frequency (count per unit length) or the degree of crimp is off specification. Such faults can be caused by improper mechanical adjustments or improper condition of the material being crimped. Absence of crimp, incorrect crimp pitch, or incorrect crimp angle in the material results in rejection of the material by customers and subsequent heavy losses to the manufacturer because of waste. The present invention provides a method and apparatus whereby such crimp may be continuously monitored, and if faulty conditions are detected, the appropriate steps can be taken before substantial loss results. Furthermore, such detection systems can be designed so that a plurality of production lines may be altemately monitored from a central location.
In accordance with the present invention, apparatus including a television camera and associated stroboscopic light are provided for producing a video signal from a portion of continuous material having surface variations, to electronically obtain useful information from such material. As described herein, the stroboscopic light is positioned at an angle such that a pattern of light and dark (shadowed) areas or strips result on the material. The video signal produced is passed through a system which uses the light and dark areas to obtain information relative to the physical properties of the material. In practice, the material is often advancing along a path which may fluctuate slightly in various directions. Such fluctuations may be caused by a number of different conditions, such as nonuniform tension on the material, variations in weight, etc. The fluctuations may interfere with obtaining the useful information, such as by giving false signals. The false signals result from unintentional shadowing of areas of the material being monitored, and produce relatively low frequency video signals. The apparatus and method herein described filters such signals from the useful signals so that much more accurate information is obtained.
2. Description of the Prior Art
Various electronic systems are presently known for detecting defects in continuous lengths of material. For example, U.S. Pat. No. 3,584,225 relates to a yarn inspection device which uses optical devices and electronic circuitry to detect defects in yarn. U.S. Pat. No. 3,114,797 relates to a television system for detecting differences or changes in shape, size, color, intensity or texture. Such differences or changes are detected by comparing a scene at one instant with an image produced from the same scene after a time delay. U.S. Pat. No. 3,700,903 relates to detection systems wherein a coherent light beam is used to scan the surface of an object in a repetitive pattern. An output signal is produced by light reflected from the object for determining characteristics of the surface of the object. The present invention provides apparatus and method for continuously monitoring continuous lengths of material, for detecting surface irregularities, obtaining data from such irregularities, and converting such data into useful information. While the prior art shows the detection of surface defects or differences, this is often not sufficient for adequate quality control. Applicant's invention provides for obtaining additional useful information from irregularities such as count and shape.